The present invention relates to a rotary pump which incorporates a pressure switch for detecting a fluid pressure variation on the pump outlet side and transmitting a detection signal.
For example, in a power steering apparatus for reducing the steering force for a vehicle, a pressure sensor is arranged in a conventional oil pump or in a pipe extending from the outlet of the pump. This pressure switch serves as a sensor for detecting an abrupt increase in oil pressure in a hydraulic circuit extending from the oil pump during a steering operation, thus increasing the idling speed of the engine to prevent an engine failure. As pressure switches of this type, switches having various structures are disclosed in, e.g., Japanese Utility Model Laid-Open Nos. 57-161840, 59-43039, and 62-57355.
More specifically, a pressure switch of this type generally includes a main body constituted by a cylindrical conductive member, a terminal embedded in one end portion of the main body to be kept insulated, and a plunger which is slidably supported in the main body and is normally biased by a spring or the like in a direction to separate from the terminal. When the oil pressure of the high-pressure side of the above-mentioned hydraulic circuit is introduced to the other end side of the plunger, and the pressure exceeds a preset pressure, the plunger is moved to the terminal connected to the atmospheric pressure. With this operation, the conductive plunger is brought into direct contact with the terminal or a conductive member is brought into indirect contact with the terminal to electrically turn on the switch, thus performing a required control operation using the resulting electrical signal.
The above-described pressure switch is generally arranged in the pump body of an oil pump as a fluid pressure source, e.g., a rotary pump such as a vane pump. This is the simplest method of arranging the pressure switch. For example, a pump having such an arrangement is disclosed in, e.g., Japanese Utility Model Laid-Open No. 63-127045. In this pump, the following components are sequentially mounted in a stepped hole formed in one end portion of the pump body: a plunger having an inner end opposing the high-pressure side, a spring retainer, a spring, a terminal opposing a plunger end portion, a plug nut fastened to the open end portion of the stepped hole to hold the terminal, and the like.
According to such an arrangement, the number of components can be decreased and a pressure switch portion protruding from the pump body side can be minimized as compared with a general arrangement in which a screw portion formed on the main body of a pressure switch separately assembled as a unit in advance is threadably engaged with a screw hole on the pump body side so as to fix the pressure switch. With this arrangement, therefore, a reduction in size and cost of the pump can be achieved.
According to the conventional structure described above, however, the pressure switch is mounted horizontally to be perpendicular to the axis of the pump regardless of the positions of a vane, a rotor, and the like as the rotating elements of the pump. For this reason, a pressure switch portion protruding to a body side portion is large, and the pressure switch tends to interfere with a vehicle bracket. Therefore, the mounting position of a pressure switch must be changed for each vehicle, requiring cumbersome operations. In addition, the number of components is large, and there is still room for improvement in its structure. Furthermore, in the conventional structure described above, since a member for holding the terminal is fixed to the pump body by using screw parts and the like, a threading operation and the like are required, posing problems in terms of practical use. Under the circumstances, demands have arisen for some measure to ensure excellent workability, facilitate the assembly of a pressure switch in a pump body, and achieve a great reduction in cost.